Process for preparing fine grained, high strength extrusions



y 1965 G. s. FOERSTER 3,181,337

PROCESS FOR PREPARING FINE GRAINED, HIGH STRENGTH EXTRUSIONS Filed Dec. '7, 1962 INVENTOR. George .5. F0 ens/er flTfORNEY United States Patent 3,181,337 PROCESS FOR PREPARING FINE GRAINED, HIGH STRENGTH EXTRUSIONS (George S. Foerster, Midland, Mich, assignor to The Dow Chemical Company, Midland, Mich, a corporation of Delaware Filed Dec. 7, 1962, Ser. No. 242,938 Claims. (Cl. 72-442) This invention relates to metal working and more specifically relates to a method of making a fine grained extrude of a magnesium base alloy.

In extruding magnesium base alloys at high tempera tures using conventional means, recrystallization and grain growth tend to occur resulting in an extruded product having poor mechanical properties. It has been found, however, that quenching the extrude immediately as it passes the die land minimizes these objectionable effects and results in a high strength fine grained extrude. Quenching of the extrude as practiced in the present art involves flooding the extrude with a liquid coolant at a point sufliciently removed from the extrusion die such that the coolant will not impinge too closely to the die lands to cause cracking of the die as a result of too rapid cooling. By the time the extrude reaches that point, however, recrystallization and grain growth at least partially occur to significantly reduce the strength of the extrude. There exists therefore a desideratum in the art for a method by which an emerging extrude can be timely and properly quenched and a fine grained extrude product produced.

The prinicpal object of the present invention, therefore, is to provide a process for making a fine grained extrude of a magnesium base alloy.

In the accompanying drawing:

FIG. 1 is a longitudinal vertical section of a die holder containing a two piece assembled die, the direction of extrusion being from right to left, said die being useful in the process of the present invention.

FIG. 2 is an interior isometric View of the exit portion of the die as assembled and shown in FIG. 1.

FIG. 3 is an interior isometric view of the entry portion of the die as assembled and shown in FIG. 1.

In practicing the method of the present invention an extrusion die is employed having an internal cooling channel relatively close to and following the outline of the extrusion aperture. The channel is provided with an inlet and an outlet, and a multiplicity of spray ports feeding from the channel and opening into a die relief cavity. A suitable coolant is circulated through said channel and a portion thereof discharged from the spray ports. A preheated billet, or batch of pellets, is then confined in the container of an extrusion machine, containing a suitable die with a coolant channel and spray ports as described above, and subjected to a suflicient displacement pressure to effect extrusion while maintaining the container temperature within the range of from about 500 F. to about 900 F. The so-heated billet is thereby expressed at least in part through the above die at the desired extrusion temperature while coolant is circulated internally through the die, with a fraction of said coolant being bled out through spray ports opening into the die relief cavity, to immediately mildly spray quench the extrude as it leaves the die land to enter said cavity.

Spray quenching in this manner with a portion of the die cooling fluid provides a mild quench almost simultaneously as the extrude leaves the die land, thereby substantially reducing the time lapse before quenching occurs to reduce grain growth. number, and location of the spray ports, and the line pressure of the coolant can be adjusted or predetermined In practice, the size,

so as to provide a uniform mild quench. If desired, a valve attached to the coolant lines may be employed to further regulate the amount of coolant bled off through the spray ports.

An example of a die which may be used in carrying out the process of the present invention is shown in the accompanying drawing. This die consists of an assembly, as shown in FIG. 1, of two portions designated an exit portion 6 shown in FIG. 2 and an entry portion 8 shown in FIG. 3. To assemble, these portions are joined as by bolting the interior surface 10 and 10 of each together. The entry portion 8 of the die contains an extrusion aperture 12 therethrough, identical to a cross-section of the desired extrusion product, the inner wall of which constitutes die lands or the forming surface of the die. The die land abruptly flares thereafter in the direction of exit to form a die relief cavity 14. The flare continues into and extends through the exit portion of the die (FIG. 2). Disposed about, but spaced from the periphery of the aperture and cavity of the entry portion is a cooling channel or groove 16, no part of which opens directly into said cavity or aperture 12. When the portions of the die are assembled, however, their interior surfaces 10 and 10 form a sealed cooling channel for circulating coolant therethrough, by means of a coolant inlet 18, and coolant outlet 20. The exit portion 6 of the die consists of the aforesaid continuation of the die relief cavity 14 and in addition is equipped with holes for a coolant inlet 18 and coolant outlet 20, each of said holes 18 and 20 being as remotely located from one another as possible in order to obtain maximum circulation in the cooling channel. Also contained in the exit portion of the die are a plurality of uniformly spaced apart spray ports 22 which communicate the cooling channel or groove 16 with the interior of the die relief cavity 14 and through which a portion, as aforesaid, of the coolant in said channel is bled off, thereby to spray and mildly quench the extrude in the die relief cavity 14 as it leaves the die lands.

The amount of coolant bled off from the channel, in order to provide a uniform mild quench, was found to be within the range from 5 to about 25 percent, preferably 15 percent, of the total amount of coolant circulated through the internal cooling channel per unit of time. Quenching in this manner also permits substantially higher extrusion speeds. If desired, mild quenching under the method described in this invention to a temperature within the range from about 300 to 700 F. at which grain growth does not occur, can be combined with an additional subsequent quench wherein the extrude is completely quenched to room temperature rather than mildly quenched as when employing singularly the method of this invention. Inasmuch as the amount of coolant bled off from the internal cooling channel when properly adjusted to accomplish a proper mild spray quench will all be evaporated and dissipated by the heat attending the extrusion process, the emerging extrude will be dry, making it unnecessary to remove excess coolant from the extrude and adjacent equipment such as, for example, the run-out table of the extrusion machine, as is, however, necessary when using conventional quenching techniques.

Any conventional extrusion die used for extruding light metals may be employed in practicing the present invention on being modified so as to provide an internal channel construction, with spray ports, substantially as described above, suflicient to accomplish the function of spray quenching the extrude in the die relief cavity thereof while also extracting heatfrom the die adjacent to the die opening.

It is understood that the coolant line pressure, size, number, and location of spray ports can be adjusted to accomplish a proper mild quenching suitable to produce a fine grained extrude article. It is usually sufiicient to spray quench the extrude down to a temperature of about 300 F. to about 700 F. from an extrusion temperature tially straight requiring no subsequent straightening procedure.

I claim:

1. A method of making a fine grained extrude article of from about 800 F. to about 1100 F. 5 a magnesium-base alloy which comprises:

In the Work leading to the present invention a die sub- (a) providing an extrusion machine containing a die stantially as described above was employed wherein the having an aperture and die land through which to spray ports were located inside the die relief cavity at a die express an extrude, an internal cooling channel point about one-half inch away from the exit die land. encircling said aperture but spaced therefrom and a In extruding the magnesium base alloy of Example I multiplicity of uniformly spaced spray ports, said through said die at about 10 f.p.m. it was found that the ports opening into a die relief cavity in the die and extrude thereby produced possessed a fine grained matrix communicating with the cooling channel; and exhibited substantially higher strength than the same (b) extruding a magnesium-base alloy through said alloy extruded without spray quenching. Data concerndie; ing this extrusion is given in Table I as part of the below (c) circulating coolant through the channel of the die example. of said extrusion machine during the extruding of The following example serves to illustrate the applicasaid alloy; tion of the present process to extruding alloys of mag- (d) bleeding off through said spray ports a portion nesium in order to obtain fine grained high strength extruof said coolant circulating through said channel; and sions. (e) discharging said portion of coolant through said EXAMPLE I spray ports onto the extruded alloy as the extrude leaves the die land and enters the die relief cavity Four extrusions of a two-leg angular section were made thcfeby p y and mildly p y quenching sitid of pelletized magnesium base alloys having the nominal trllde and Producing a fine grained extrude armlecomposition of 6 precent zinc, 0.6 percent zirconium, 2. The method of claim 1 wherein the amount of coolthe balance being magnesium, from a 3 inch diameter ant bled off through the spray ports to mildly spray quench container by the method of the present invention using the extrude is from about 5 to about 25 percent by volume a die constructed with a cooling channel, and spray ports of the total amount of coolant supplied to the internal of 0.020 inch in diameter. Two of the extrusions were cooling hannel. made with Water flowing at 70 to 80 P- e through the 3. The method of claim 1 wherein the extruding is internal channel of the die at 2.67 gallons per minute of arried out at a temperature of from about 500 F. to which 0.37 gallon per minute was diverted through the about 900 F, and the extrude is mildly spray quenched spray ports onto the extrude, thereby partially quenching to a temperature of from about 300 F. to about 700 F. the extrude. The other two were made without the 4. A method of making a fine grained extruded article water flowing in the die. One extrusion of each group of a magnesium-base alloy which comprises: was externally water quenched by using conventional (a) providing an extrusion machine containing a die quenching equipment located at about 3 /2 inches from having an aperture and die land through which to the die. The extrusion temperature, and rate, was at die express an extrude, an internal cooling channel 700 F. and 10 f.p.m. respectively. Samples were taken encircling said aperture and a multiplicity of unifrom the middle and butt of each extrusion and tested in formly spaced spray ports, said ports opening into a respect to both the thin and thick section as extruded and die relief cavity in the die and communicating with also after aging 24 hours at 300 F. the cooling channel;

Table I sets forth the compressive yield strength, re- (b) extruding a magnesium-base alloy through said corded as a result of the above test for each of the two die at a temperature of from about 500 F. to about legs of the angular section. 900 B;

Table I Compressive Yield Strength 1 No leg lie leg Spray N0 Spray External External Quench Quench Quench Quench Middle Butt Middle Butt FT5FT5FT5FT5 42 47 42 4e 43 44 40 43 as 48 a7 42 33 as 37 41 35 as 39 4s 35 37 39 45 30 36 F =as fabricated.

T5=aged 24 hours at 300 F.

1 In thousands of pounds.

From a comparison of the figures shown for Examples (0) circulating coolant through the channel of the 1 and 2, wherein spray quenching was employed, with die of said extrusion machine during the extruding the figures shown for Examples 3 and 4, wherein no spray of said 3; quenching was employed, the resulting superior strength Pleedmg ofifhroug'h Sald p y PP a Portion of of the extrudes in the first two examples is apparent and 531d coolant clrculatmg through 531d channel in an represents a significant improvement by using the process amount of from about 5 to about 5 percent by volof the present invention. ume of the total amount of coolant supplied to the When employin conventional quenching techniques channel;

Hall the extrud: is War ed and therefore must (e) discharging said amount of coolant bled-off through us y P said spray ports onto the extruded alloy as it leaves Stralghtened' In some cases thls Warping 15 so the die land and enters the die relief cavity thereby severe that the extrude cannot be adequately straightened. mildly Spray quenching Said extrude to a temperature W11e11 emlfloyillg Spray queflchlng under the method of within the range of from about 300 F. to about the present invention, however, the extrudes are substan- 700 F.

5 5. The method of claim 4 wherein about 15 percent of the coolant supplied to the cooling channel is bled off through the spray ports to rapidly and mildly spray quench the extrude.

References Cited by the Examiner UNITED STATES PATENTS 6 Hyprath 20716 Leontis et a1 20710.2 Haendeler 20716 Zipf 20710 MICHAEL V. BRINDSI, Primary Examiner.

CHARLES W. LANHAM, Examiner. 

1. A METHOD OF MAKING A FINE GRAINED EXTRUDE ARTICLE OF A MAGNESIUM-BASE ALLOY WHICH COMPRISES: (A) PROVIDING AN EXTRUSION MACHINE CONTAINING A DIE HAVING AN APERTURE AND DIE LAND THROUGH WHICH TO DIE EXPRESS AN EXTRUDE, AND INTERNAL COOLING CHANNEL ENCIRCLING SAID APERTURE BUT SPACED THEREFROM AND A MULTIPLICITY OF UNIFORMLY SPACED SPRAY PORTS, SAID PORTS OPENING INTO A DIE RELIEF CAVITY IN THE DIE AND COMMUNICATING WITH THE COOLING CHANNEL; (B) EXTRUDING A MAGNESIUM-BASE ALLOY THROUGH SAID DIE; (C) CIRCULATING COOLANT THROUGH THE CHANNEL OF THE DIE OF SAID EXTRUSION MACHINE DURING THE EXTRUDING OF SAID ALLOY; (D) BLEEDING OFF THROUGH SAID SPRAY PORTS A PORTION OF SAID COOLANT CIRCULATING THROUGH SAID CHANNEL; AND (E) DISCHARGING SAID PORTION OF COOLANT THROUGH SAID SPRAY PORTS ONTO THE EXTRUDED ALLOY AS THE EXTRUDE LEAVES THE DIE LAND AND ENTERS THE DIE RELIEF CAVITY THEREBY RAPIDLY AND MILDLY SPRAY QUENCHING SAID EXTRUDE AND PRODUCING A FINE GRAINED EXTRUDE ARTICLE. 